Nano-Particles of Molybdenum Oxide

ABSTRACT

Nano-particle of MoO 3 . The nano-particle of the present invention has a surface area in the range of 33 to about 68 m 2 /g as determined by BET. The nano-particle may also have a rod-like non-hollow configuration.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of U.S. patent application Ser. No. 10/438,597, filedMay 15, 2003, which is a continuation-in-part of U.S. patent applicationSer. No. 10/222,626, filed Aug. 16, 2002, which is a divisional of U.S.patent application Ser. No. 09/709,838, filed on Nov. 9, 2000, now U.S.Pat. No. 6,468,497 B1, both of which are incorporated herein byreference for all that they disclose.

FIELD OF INVENTION

This invention relates to the production of nano-particles in generaland more particularly to a method and apparatus for producingnano-particles of molybdenum oxide.

BACKGROUND

Nano-particles, that is, particles having average sizes less than about1 micrometer (i.e., 1 micron) are known in the art and are of interestbecause their nano-crystalline and/or other nano-scale featuresdramatically change the properties of the material. For example, certainmaterials fabricated from nano-particles often possess superiormechanical properties compared with the same material fabricated in aconventional manner and with conventionally-sized starting materials(e.g., powders). Nano-particles of other materials may also possessunique electrical and/or magnetic properties, thereby opening the doorto the fabrication of materials having previously unforeseen propertiesand attributes. The extremely large surface area to weight ratio ofnano-particles allows nano-particles to interact with their surroundingsvery quickly which can also lead to the fabrication of new materialshaving new properties.

In sum, it is recognized that the ability to produce any material innano-particle form represents a unique opportunity to design and developa wide range of new and useful mechanical, optical, electrical, andchemical applications, just to name a few. However, one problem thatheretofore has limited the use of nano-particles is the difficulty inproducing nano-particles of the desired size and composition on acommercial scale, e.g., by the kilogram instead of by the gram.

One method for producing nano-particles involves dissolving in a solventprecursor chemicals which define the composition of the finalnano-particle product. The resulting composition is mixed to yield asolution which is substantially homogenous on a molecular level. Thesolvent is then evaporated at a sufficient rate so that the componentsin the homogenized solution are precipitated as a homogenized solidpowder. While such wet processes have been used to producenano-particles of various compositions, they are not without theirproblems. For example, such processes tend to produce larger particlesalong with the nano-particles, which must then be removed or separatedfrom the nano-particles before the nano-particles can be used. Such wetprocesses can also involve a significant number of process steps andreagents which tend to increase the overall cost of the finalnano-particle product.

Another method for producing nano-particles is a primarily mechanicalprocess in which the precursor material is ground in a mill (e.g., aball mill) until particles of the desired size are produced.Unfortunately, however, such grinding processes are energy intensive,require substantial amounts of time, and typically result in theproduction of a powder containing not only the desired nano-particleproduct, but also particles having larger sizes as well. Of course, suchlarger sized particles must be separated from the nano-particles beforethey can be used. The abrasive materials used in such milling andgrinding processes also tend to contaminate the nano-particle material.Consequently, such grinding processes generally are not conducive to theproduction of a highly pure nano-particle product.

Several other processes have been developed in which the precursormaterial is vaporized, typically in a partial vacuum, and then rapidlycooled in order to initiate nucleation and precipitate the nano-particlematerial. For example, in one process, a stream of vaporized precursormaterial is directed onto the surface of a cold (i.e., refrigerated)rotating cylinder. The vapor condenses on the cold surface of thecylinder. A scraper placed in contact with the rotating cylinder scrapesoff the condensed material, which is then collected as the nano-particleproduct. In another process, the vapor stream of precursor material iscondensed by expanding the vapor stream in a sonic nozzle. That is, thevapor stream is initially accelerated in the converging portion of thenozzle, ultimately reaching sonic velocity in the throat of the nozzle.The vapor stream is then further accelerated to a supersonic velocity inthe diverging section of the nozzle. The supersonic expansion of thevapor stream rapidly cools the vapor stream which results in theprecipitation of nano-sized particles.

While the foregoing vaporization and cooling processes have been used toproduce nano-particle materials, they are not without their problems.For example, the rotating cold cylinder process has proved difficult toimplement on a large scale basis and has been less than successful inproducing large quantities of nano-particle material. While the sonicnozzle process is theoretically capable of producing large quantities ofnano-particles on a continuous basis, it requires the maintenance of aproper pressure differential across the sonic nozzle throughout theprocess. Another problem with the sonic nozzle process is that thenano-particle material tends to condense on the nozzle walls, which canseriously reduce the efficiency of the nozzle, and may even prevent itfrom functioning. While the condensation problem can be reduced byinjecting a boundary layer stream along the nozzle walls, such aprovision adds to the overall complexity and operational cost of thesystem.

Consequently, a need remains for a method and apparatus for producingnano-particles that does not suffer from the shortcomings of the priorart methods. Such a method and apparatus should be capable of producinglarge quantities of nano-particle product, preferably on a continuousbasis, and at a low cost. Ideally, such a method and apparatus should beless sensitive to certain process parameters than other systems, therebyallowing the method and apparatus to be more easily practiced on a largescale (i.e., commercial) basis. Additional advantages could be realizedif the method and apparatus produced nano-particles in a relativelynarrow size range, with a minimum amount of larger sized particlesand/or contaminant materials.

SUMMARY OF THE INVENTION

A nano-particle of MoO₃ according to the present invention has surfacearea in the range of 33 to about 68 m²/g as determined by BET. Inanother embodiment, the nano-particle of MoO₃ may have a generallycylindrically shaped rod-like non-hollow configuration. Further, thenano-particle of the present invention may also have a configuration inwhich a mean length that is greater than a mean diameter. In anotherembodiment, the nano-particle of MoO₃ may have blunt ends.

In another embodiment, the nano-particle of MoO₃ has a surface area inthe range of 45 to about 68 m²/g as determined by BET. In anotherembodiment, the nano-particle of MoO₃ further has a generallycylindrically shaped rod-like non-hollow configuration.

BRIEF DESCRIPTION OF THE DRAWING

Illustrative and presently preferred embodiments of the invention areshown in the accompanying drawing in which:

FIG. 1 is a schematic representation of the apparatus for producingnano-particles according to one embodiment of the invention;

FIG. 2 is a cross-sectional view in elevation of the precipitationconduit in which the nano-particles are formed;

FIG. 3 is a cross-sectional view in elevation of the product collectionmanifold;

FIG. 4 is a transmission electron microscope image of an MoO₃nano-particle product produced by the present invention;

FIG. 5 is schematic representation of the apparatus for producingnano-particles according to another embodiment of the invention; and

FIG. 6 is a transmission electron microscope image of an MoO₃nano-particle produced by the embodiment of the invention illustrated inFIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Apparatus 10 for producing nano-particles of a precursor material isshown and described herein as it may be used to produce nano-particles12 (FIGS. 2-4) of molybdenum oxide (MoO₃) from a precursor material 14.Alternatively, the apparatus 10 may be used to produce nano-particles ofother vaporizable or sublimable materials, as will be described ingreater detail below. In the embodiment shown and described herein, theapparatus 10 for producing nano-particles 12 may comprise a sublimationfurnace 16 having at least one vapor region 18 associated therewith. Aprecipitation conduit 20 having an inlet end 22 and an outlet end 24extends into the vapor region 18 so that the inlet end 22 ofprecipitation conduit 20 is exposed to vaporized (e.g., sublimated)material 36 contained within the vapor region 18. The outlet end 24 ofconduit 20 is connected to a product collection apparatus 26 whichcollects the nano-particle product 12.

The inlet end 22 of precipitation conduit 20 is best seen in FIG. 2 anddefines an isolation chamber 28 within which is provided a quench fluidport 30. The quench fluid port 30 is connected to a supply of a quenchfluid 32, such as liquid nitrogen. See FIG. 1. The quench fluid 32 isdischarged from the quench fluid port 30 as a fluid stream 34. As willbe described in greater detail below, the fluid stream 34 rapidly coolsthe vaporized material 36 flowing through the precipitation conduit 20.This rapid cooling results in the precipitation of the nano-particlematerial 12 within the precipitation conduit 20. The precipitatednano-particle material 12 continues to be carried along theprecipitation conduit 20 to the product collection apparatus 26.

The product collection apparatus 26 may comprise a filter assembly 40and a pump assembly 42 that is fluidically connected to the filterassembly 40. The pump assembly 42 draws or pumps the vaporized material36 from the vapor region 18, into the precipitation conduit 20, andultimately through the filter assembly 40. More specifically, thevaporized material 36 is converted within the precipitation conduit 20into a carrier stream having the nano-particle material 12 suspendedtherein. The carrier stream containing the suspended nano-particlematerial 12 continues to be drawn through the precipitation conduit 20under the action of pump 42, ultimately reaching the filter assembly 40.The filter assembly 40 removes the nano-particle material 12 from thecarrier stream. The carrier stream is then discharged into thesurrounding atmosphere as filtered carrier stream 68.

The apparatus 10 for producing nano-particles may be operated as followsto produce nano-particles of molybdic oxide (MoO₃). As a first step inthe process, a suitable MoO₃ precursor material 14, such as MoO₂ orMoO₃, is fed into the sublimation furnace 16. The MoO₃ precursormaterial 14 is sublimed (i.e., converted directly to a vapor or gasstate from a solid state without passing through a liquid state) withinthe sublimation furnace 16, resulting in the production of a sublimed orvapor state material 36. The sublimed or vapor state material 36 isgenerally contained within the vapor region 18. Depending on thecomposition of the precursor material 14, the sublimed (i.e., vaporized)material 36 may be combined with a suitable oxygen-containing carriergas 38 (e.g, air) in order to fully oxidize the sublimed material. Thecarrier gas 38 may be allowed to enter the vapor region 18 through asuitable opening 70 provided therein. Such additional oxidation may berequired or desired if the precursor material comprises “sub-oxide”material (e.g, MoO₂) and where the nano-particle material 12 is to beMoO₃.

Once the pump 42 of the product collection apparatus 26 is activated, itdraws the sublimed or vaporized material 36 contained within the vaporregion 18 into the inlet end 22 of precipitation conduit 20. Thesublimed material 36 first enters the isolation chamber 28 (FIG. 2)which isolates the sublimed material from the vapor region 18. As thesublimated material 36 continues to flow through the conduit 20, thesublimed material 36 contacts and mixes with the quench fluid stream 34emerging from the quench fluid port 30. The fluid stream 34 rapidlycools or quenches the sublimated material 36 (i.e., substantiallyadiabatically) which causes the precipitation of the nano-particlematerial 12. The precipitated nano-particle material 12 is generallysuspended within a carrier stream (which may comprise air and/or othergaseous components remaining in the vapor stream 36 after theprecipitation of the nano-particle material 12). Thereafter, the carrierstream containing the precipitated nano-particle material 12 continuesto be carried along the conduit 20, whereupon it is ultimately collectedby the filter 40 in the product collection apparatus 26. The filter 40may be harvested from time to time to remove the accumulatednano-particle material 12.

The nano-particle material 12 of MoO₃ produced according to the methodand apparatus of the present invention may be imaged in accordance withany of a wide range of microscopy processes that are now known in theart or that may be developed in the future that are suitable for imagingparticles in the nano-size range. For example, FIG. 4 is an image of thenano-particle material 12 produced by a transmission electron microscopein a process generically referred to as transmission electron microscopy(TEM). As is readily seen in the TEM image illustrated in FIG. 4, eachindividual particle of the nano-particle material 12 comprises agenerally cylindrically shaped, rod-like configuration having a meanlength that is greater than the mean diameter. While the size of thenano-particle material 12 can be expressed in terms of the mean lengthor the mean diameter of the particles (e.g., as imaged by transmissionelectron microscopy), it is generally more useful to express the size ofthe nano-particle material 12 in terms of surface area per unit weight.Measurements of particle surface area per unit weight may be obtained byBET analysis. As is well-known, BET analysis involves an extension ofthe Langmiur isotherm equation using multi-molecular layer absorptiondeveloped by Brunauer, Emmett, and Teller. BET analysis is anestablished analytical technique that provides highly accurate anddefinitive results. In the embodiment shown and described herein, themethod and apparatus of the present invention has produced nano-particlematerial having sizes in the range of about 4-44 square meters/gram(m²/g) (15-35 m²/g preferred) as measured in accordance with BETanalysis. Alternatively, other types of measuring processes may be usedto determine the particle size.

A significant advantage of the present invention is that it can be usedto produce nano-particles of MoO₃ in very large quantities and at a verylow cost. The present invention is also relatively simple to construct,easy to operate, and is not overly sensitive to certain processparameters. Consequently, the present invention is ideally suited foruse in large-scale (i.e., commercial) applications. The nano-particlematerial 12 produced by the present invention also contains particleswithin a fairly narrowly defined size range and with a minimum amount oflarger-sized particles. Consequently, the nano-particle material 12produced in accordance with the method and apparatus of the presentinvention may be generally regarded as a high quality product thatrequires little or no additional processing before it may be used.

Another advantage of the present invention is that it is generallyimmune to problems associated with the condensation of the nano-particlematerial on the internal components of the precipitation conduit 20.Consequently it is not necessary to take additional measures (e.g., theinjection of an insulating boundary layer) to discourage theaccumulation of nano-particle material on the internal components of thesystem. Moreover, even if the nano-particle product eventuallyaccumulates on the internal components of the system, the simple designof the system will allow any such accumulation to be easily removed.

Still yet other advantages are associated with the quench fluid tube 54.For example, the quench fluid tube 54 may be readily fabricated fromcommonly available tubing and does not require the provision of anyconverging/diverging sections. The placement of the quench fluid tube 54within the inner pipe member 46 further simplifies construction of thenano-particle apparatus.

Having briefly described the method and apparatus according to oneembodiment of the present invention, as well as some of their moresignificant features and advantages, the various embodiments of themethod and apparatus for producing nano-particles of the presentinvention will now be described in detail.

Referring back now to FIG. 1, one embodiment of the apparatus 10 forproducing nano-particles is shown and described herein as it may be usedto produce nano-particles 12 of molybdenum tri-oxide (MoO₃).Alternatively, however, the present invention could also be used toproduce nano-particles of other vaporizable or sublimable materials, aswould be obvious to persons having ordinary skill in the art afterhaving become familiar with the teachings of the present invention. Theapparatus 10 may comprise a sublimation furnace 16 having a vapor region18 associated therewith. The sublimation furnace 16 is suitable forreceiving a supply of the precursor material 14. The precursor material14 may be delivered to the furnace 16 in either a continuous manner orin batches. For example, in one preferred embodiment, the precursormaterial 14 is fed into the sublimation furnace 16 on a continuous basisby a screw-type conveyor system 60. Alternatively, of course, otherprecursor materials, vaporizing devices and/or product deliveryschedules may also be used.

In the embodiment shown and described herein, the sublimation furnace 16comprises an electrically heated furnace having one or more electricheating elements 50 provided therein for elevating the temperature inthe sublimation furnace 16 to a level sufficient to sublimate theprecursor material 14. As is commonly understood, the terms “sublimate”or “sublimation” refer to processes wherein a material is transformeddirectly from the solid state to the gas or vapor state without passingthrough the liquid state. Sublimation of the precursor material 14allows for the production of a highly pure MoO₃ product.

As an aside, it should be noted that while sublimation furnaces arecurrently used to produce highly purified MoO₃ powder (conventionallyreferred to as sublimed molybdic oxide), the particles comprising theresulting powder produced by currently used sublimation processes areconsiderably larger than the nano-sized particles produced with themethod and apparatus of the present invention.

Continuing now with the description, it should be noted that the presentinvention is not limited to use with sublimation furnaces, but couldinstead utilize any of a wide range of other furnaces that are now knownin the art or that may be developed in the future that are or would besuitable for vaporizing or sublimating the precursor material 14.Examples of other types of furnaces that could be utilized with thepresent invention include, but are not limited to, muffle furnaces,induction furnaces, vacuum furnaces, plasma arc furnaces, tube furnaces,and arc furnaces. Consequently, the present invention should not beregarded as limited to the sublimation furnace 16 that is shown anddescribed herein.

As will be discussed in greater detail below, the furnace 16 may beprovided with one or more openings or inlets 70 therein to allow acarrier gas 38 to enter the sublimation region 18. Depending on theapplication, the carrier gas could comprise an oxidizing gas, a reducinggas, or an inert gas. Stated another way, the inlet 70 and theparticular carrier gas 38 that is allowed therein allow the vaporizationor sublimation process to occur within a controlled gas atmosphere. Inthe embodiment shown and described herein, the carrier gas 38 is air, sothe inlet 70 may be open to the surrounding atmosphere.

With reference now to FIGS. 1 and 2, the precipitation conduit 20 ispositioned within the sublimation furnace 16 so that the inlet end 22 ofprecipitation conduit 20 is contained generally within the vapor region18 defined by the furnace 16. The outlet end 24 of the precipitationconduit 20 may be connected to a collection manifold 44 which is thenconnected to the product collection system 26. See FIG. 1.Alternatively, the outlet end 24 of precipitation conduit 20 may beconnected directly to the product collection system 26.

The precipitation conduit 20 may comprise a generally elongate,pipe-like member 46 that defines the inlet end 22 and the outlet end 24(FIG. 3) of precipitation conduit 20. The elongate, pipe-like member 46may be supported along at least a portion of its length by a generallyelongate, pipe-like outer member 48, as best seen in FIG. 1. In theembodiment shown and described herein, pipe-like outer member 48 isgenerally concentrically aligned with pipe-like inner member 46 and isseparated a spaced distance therefrom so that an insulating space orannulus 52 is defined between the inner and outer pipe-like members 46and 48. See FIG. 2. The insulating annulus 52 is advantageous in that ithelps to keep the inner pipe-like member 46 cool, thereby discouragingthe re-vaporization of the precipitated nano-particle material 12flowing through the inner pipe 46.

The inner and outer pipe-like members 46 and 48 may be fabricated fromany of a wide variety of materials (e.g., high-temperature alloys andstainless steels) suitable for the intended application. By way ofexample, in one preferred embodiment, the inner pipe member 46 isfabricated from a high-temperature alloy (e.g., Hastelloy® “C”) sincethe inlet end 22 of inner pipe 46 is exposed to the high temperatures inthe vapor region 18. The outer pipe-like member 48 is fabricated fromtype SAE 316 stainless steel, although it could also be fabricated fromother types of steel alloys.

The inner and outer pipe-like members 46 and 48 may have dimensions thatare commensurate with the size (i.e., desired production capacity) ofthe apparatus 10 for producing nano-particles. In the embodiment shownand described herein, the inner pipe-like member 46 has an insidediameter of about 41.3 mm and a wall thickness of about 6.4 mm. Theouter pipe-like member 48 may have an inside diameter of about 54 mm anda wall thickness of about 6 mm. Accordingly, the insulating space orannulus 52 will have a thickness of about 7 mm.

As was briefly described above, the inner, pipe-like member 46 isprovided with a quench fluid port 30 that is suitable for dischargingthe quench fluid stream 34 into the inner, pipe-like member 46. See FIG.2. In the embodiment shown and described herein, the quench fluid port30 may comprise an elongate tube-like member or quench fluid tube 54having an inlet end 56 and a J-shaped outlet end 58. The inlet end 56 ofquench fluid tube 54 is connected to the supply of quench fluid 32,preferably via an accumulator 62. Accumulator 62 ensures that the quenchfluid 32 (e.g., a cryogenic gas) supplied to the inlet end 56 of quenchfluid tube 54 remains in the liquid state. The J-shaped outlet end 58 ofquench fluid tube 54 defines the fluid port 30 and is positioned withinthe isolation chamber 28 so that the fluid port 30 is directed towardthe outlet end 24 of precipitation conduit 20. Consequently, the quenchfluid stream 34 discharged by the fluid port 30 is directed generallytoward the outlet end 24 of precipitation conduit 20. See FIG. 3.

The location of the quench fluid port 30 within the isolation chamber 28has some influence on the sizes of the nano-particles 12 produced by theapparatus 10 according to the present invention. For example, moving thelocation of the fluid port 30 closer to the inlet end 22 ofprecipitation conduit 20 generally results in larger nano-particles 12being produced. Conversely, moving the location of the fluid port 30away from the inlet end 22 generally results in smaller nano-particles12. However, other factors can also affect the particle size. Forexample, smaller nano-particles can be produced even when the fluid port30 is positioned closer to the inlet end 22 of fluid conduit 20 byincreasing the flow rate of the product collection device 26. That is,higher flow rates (e.g., in liters/minute) will result in a highervelocity flow within the precipitation conduit 20. Of course, thevelocity within the precipitation conduit 20 can also be changed byvarying the inside diameter of the inner pipe 46. In another embodiment,the quench fluid port 30 may be positioned within the collectionmanifold 44. If so, the collection manifold 44 is regarded as part ofthe precipitation conduit. However, we have found that it is generallypreferable to position the quench fluid port 30 within the precipitationconduit 20 in the manner shown and described herein.

Since the sizes of the nano-particles produced by the apparatus of thepresent invention are related to several structural and operationalparameters of the invention, as described herein, the present inventionshould not be regarded as limited to any particular parameters or rangeof parameters for any given structural or operational configuration. Forexample, in the embodiment shown and described herein, the quench fluidport 30 is positioned within the isolation chamber 28 so that quenchfluid port 30 is located about 16.5 cm from the inlet end 22 ofprecipitation conduit 20. This position, combined with the otherparameters specified herein, will result in the formation of anano-particle product substantially as described herein. However,depending on the flow rate provided by the product collection system 26,good results have also been obtained by positioning the quench fluidport 30 in the range of about 150-360 mm from the inlet end 22 ofprecipitation conduit 20. As mentioned above, it is also possible toposition the quench fluid port 30 within the collection manifold 44, andsuch a positioning may be advantageous depending on the particularnano-particle product that is to be produced as well as on certain otherprocess parameters.

The quench fluid tube 54 may be made from any of a wide range ofmaterials (e.g., stainless steels) that would be suitable for theintended application. By way of example, the quench fluid tube 54utilized in one embodiment of the invention is fabricated from type SAE316 stainless steel. The size (i.e., inside diameter) of the quenchfluid tube 54 may vary depending on the size (i.e., overall productioncapacity) of the apparatus 10. In the embodiment shown and describedherein, the quench fluid tube 54 has an inside diameter of about 4 mm.Alternatively, of course, other tube sizes may be used, as would beobvious to persons having ordinary skill in the art after having becomefamiliar with the teachings of the present invention.

While the quench fluid port 30 in one embodiment of the invention isprovided by means of the J-shaped outlet end 58 of the quench fluid tube54, other configurations are possible. For example, in anotherembodiment, the inner pipe 46 is provided with an integral flow channeltherein that terminates in a discharge arm having a fluid outlettherein. The discharge arm may be generally radially oriented within theisolation chamber defined by the inner pipe and the fluid outlet may bepositioned so that it is generally aligned with the central axis of theinner pipe. Such an arrangement allows the quench fluid to be dischargedat about the center of the inner pipe.

It is generally preferred, but not required, to position a temperaturesensor, such as a thermocouple (not shown) within the interior region ofthe precipitation conduit 20 at a location downstream of the quenchfluid port 30 (i.e., between the quench fluid port 30 and the outlet end24 of conduit 20). The output signal (not shown) from the thermocouple(also not shown) may then be monitored to maintain the temperature ofthe carrier stream and suspended nano-particle product 12 within adesired temperature range that is appropriate for the particularnano-particle material 12 being produced. By way of example, in onepreferred embodiment, the thermocouple is positioned about 240 mmdownstream of the quench fluid port 30. Alternatively, the thermocouplemay be located at other positions.

The collection manifold 44 is best seen in FIG. 3 and serves as aconvenient means for directing the nano-particles toward the productcollection system 26 while allowing the supply of quenching fluid 32 tobe directed into the quench fluid tube 54. More specifically, in theembodiment shown and described herein the collection manifold 44 definesan interior chamber 64 having an outlet end 66 that is connected to theproduct collection system 26. The outlet end 24 of the inner pipe 46 ofprecipitation conduit 20 terminates within the interior chamber 64 sothat nano-particle material 12 exiting the precipitation conduit 20 isconveyed to the outlet end 66 of collection manifold 44. The outersupport pipe 48 of precipitation conduit 20 may be secured to thecollection manifold 44 (e.g., by welding) to allow the collectionmanifold 44 to be supported by the outer support pipe 48. The quenchfluid tube 54 may pass through the collection manifold 44 where it isultimately connected to the accumulator 62.

The collection manifold 44 may be fabricated from any of a wide range ofmaterials suitable for the intended application, as would be obvious topersons having ordinary skill in the art after having become familiarwith the teachings of the present invention. By way of example, in onepreferred embodiment, the collection manifold 44 is fabricated from typeSAE 316 stainless steel, although other mild steel alloys, ceramics, orother suitable materials may also be used.

The product collection system 26 is best seen in FIG. 1 and may comprisea blower or pump 42 and filter assembly 40. The blower or pump 42 drawsthe vaporized precursor material 36 through the precipitation conduit20, the collection manifold 44, and filter assembly 40. More precisely,the vaporized material 36 is converted within the precipitation conduit20 into a carrier stream having the nano-particle material 12 suspendedtherein. The carrier stream containing the suspended nano-particlematerial 12 continues to be drawn through the precipitation conduit 20under the action of pump 42, ultimately reaching the filter assembly 40.The filter assembly 40 removes the nano-particle material 12 from thecarrier stream. The carrier stream is then discharged into thesurrounding atmosphere as filtered carrier stream 68. The filterassembly 40 may be harvested from time to time to remove the capturednano-particle material 12.

The blower or pump 42 utilized in the product collection system 26 maycomprise any of a wide range of air pump devices that are well-known inthe art and readily commercially available. By way of example, in onepreferred embodiment, the pump 42 comprises a centrifugal blower havinga capacity of about 2800 (e.g., 2831) liters per minute. Alternatively,the pump 42 may have either a larger or smaller capacity depending onthe intended production capacity of the nano-particle productionapparatus 10. In another embodiment, the pump 42 may be provided with avariable capacity to allow the user to vary the flow rate of the pump 42to more easily effect certain changes in the sizes of the nano-particlematerial 12.

The filter assembly 40 may comprise any of a wide range devices suitablefor removing small particles from an air stream. By way of example, inthe embodiment shown and described herein, the filter assembly 40comprises a particulate filter medium fabricated from Gore-Tex®. Thefilter material should be sufficiently fine so that it will capturesubstantially all of the nano-particle material 12 exiting thecollection manifold 44. However, since filters for capturing suchnano-sized particles are well-known in the art and could be easilyprovided by persons having ordinary skill in the art after having becomefamiliar with the teachings of the present invention, the filterutilized in one preferred embodiment of the present invention will notbe described in further detail herein.

In an alternative arrangement, the filter assembly 40 may comprise aliquid scrubber-type filter wherein the nano-particle material 12 iscollected by bubbling the carrier stream and nano-particle material 12through a liquid (e.g., alcohol), although other liquids may be used.The liquid captures the nano-particle material which may thereafter beremoved from the liquid by conventional techniques. Still otherfiltering devices and processes are possible and could be used tocapture and remove the nano-particle product 12 from the carrier stream,as would be obvious to persons having ordinary skill in the art afterhaving become familiar with the teachings of the present invention.Consequently, the present invention should not be regarded as limited tothe particular product collection apparatus shown and described herein.

The supply of quench fluid 32 may comprise a supply of a fluid suitablefor effecting the rapid (i.e., substantially adiabatic) cooling of thevaporized precursor material 36. Toward this end, it is generallypreferable that the supply of quench fluid 32 comprise a supply of acryogenic fluid. As used herein, the term “cryogenic fluid” refers to aliquids that boil at temperatures of less than about 110 K (−163.15° C.)at atmospheric pressure. Cryogenic fluids include, but are not limitedto, hydrogen, helium, nitrogen, oxygen, argon air, and methane. In theembodiment shown and described herein, the supply of quench fluid 32comprises a supply of liquid nitrogen. In order to provide optimalquenching performance, it is generally preferable to place anaccumulator 62 between the supply of quench fluid 32 and the inlet 56 ofquench fluid tube 54. The accumulator 62 helps to ensure that the quenchfluid enters the tube 54 as a liquid, as opposed to a liquid/gasmixture. Alternatively, a liquid/gas mixture can be used if increasedflow-rates are desired and the end temperature is maintained within theappropriate range. Accordingly, the quench fluid 32 may enter the quenchfluid tube 54 as either a pure liquid, a pure gas, or a mixture thereofso long as the temperature sensed by the thermocouple (not shown)positioned within the precipitation conduit 20 is maintained at theappropriate temperature for the particular nano-particle material 12.

The accumulator 62 may comprise any of a wide range of accumulators thatare well-known in the art and that are readily commercially available.Consequently, the accumulator 62 that may be utilized in one preferredembodiment of the invention will not be described in greater detailherein.

The apparatus 10 may be operated in accordance with the following methodin order to produce nano-particles 12 of MoO₃. The nano-particles 12 ofMoO₃ are produced from a precursor material 14 that may comprise any ofa wide range of molybdenum compounds and oxides that are convertibleinto MoO₃. For example, in one preferred embodiment, the precursormaterial may comprise a so-called “technical grade” molybdic oxide(MoO₃) powder having a typical size of about 200 U.S. Tyler mesh andpreferably less than about 100 U.S. Tyler mesh. The technical grademolybdic oxide (MoO₃) precursor material 14 may be produced inaccordance with any of a variety of processes that are well-known in theart, such as roasting processes and so-called “wet” processes. Forexample, the MoO₃ precursor material 14 may be produced according to theprocess disclosed in U.S. Pat. No. 5,804,151, entitled “Process forAutoclaving Molybdenum Disulfide” issued Sep. 8, 1998, which is herebyincorporated herein by reference for all that it discloses.Alternatively, the MoO₃ precursor material 14 may be produced accordingto the process disclosed in U.S. Pat. No. 5,820,844, entitled “Methodfor the Production of a Purified MoO₃ Composition,” issued Oct. 13,1998, which is also incorporated herein by reference for all that itdiscloses. Technical grade MoO₃ powder is also readily commerciallyavailable from the Climax Molybdenum Company of Ft. Madison, Iowa, 52627(USA), which is a subsidiary of Phelps Dodge Corporation.

Other precursor materials are available and could also be used inconjunction with the present invention, as would be obvious to personshaving ordinary skill in the art after having become familiar with theteachings of the present invention. For example, in another embodiment,the precursor material 14 may be comprised entirely of molybdenum“sub-oxides” (e.g., MoO₂), or some combination of molybdenum“sub-oxides” and MoO₃. If so, the amount of molybdenum sub-oxides may besubsequently oxidized by providing an oxidizing atmosphere in the vaporregion 18. The oxidizing atmosphere will oxidize any sub-oxidescontained in the precursor material 36 before the same is drawn into theprecipitation conduit 20. Additional oxygen for the oxidization processmay be obtained from the carrier gas 38 (e.g., air) that is allowed toenter the vapor region 18 of the sublimation furnace 16 via the carriergas inlet 70. Alternatively, a separate supply of an oxygen-containinggas may be provided to the vapor region 18 in order to provide theoxidizing atmosphere required to fully oxidize any sub-oxide compoundsthat may be present. Of course, the carrier gas could comprise othermaterials depending on the particular process. For example, the carriergas 38 could also comprise a reducing gas or an inert gas.

Regardless of the particular precursor material 14 that is utilized(e.g., either MoO₃ or MoO₂), the precursor material 14 may be fed intothe sublimation furnace 16 in either a continuous manner or in batches.In the embodiment shown and described herein, the precursor material 14is fed into the furnace 16 in a continuous manner by a screw-typeconveyer system 60. Once the precursor material 14 is delivered to thesublimation furnace 16, the sublimation furnace 16 heats the precursormaterial 14 to a temperature in the range of about 800°-1300° C. (withoptimum results being obtained within a temperature range of about1093°-1260° C.), which is sufficient to sublime the MoO₃ precursormaterial 14, resulting in the production of a vaporized or sublimedprecursor material 36. As mentioned above, sublimation is a processwherein the precursor material transitions to a gaseous or vapor statedirectly from a solid state without passing through a liquid state.Sublimation of the precursor material 14 allows the production of ahighly purified nano-particle product 12.

The sublimed or vaporized precursor material 36 may be combined with acarrier gas 38, such as air or any other desired atmosphere, to assistin the flow of the vaporized or sublimed precursor material 36 into theinlet end 22 of the precipitation conduit 20. As mentioned above, thecarrier gas 38 may serve as a source of additional oxygen to oxidize anysub-oxides that may be contained in the vaporized precursor material 36.Alternatively, the carrier gas 38 may comprise an inert gas or may besupportive of reduction reactions if required or desired. The vaporizedprecursor material 36 (along with the carrier gas 38) is drawn into theinlet end 22 of the precipitation conduit 20 by the action of pump 42.Upon being drawn into the inlet end 22 of precipitation conduit 20, thevaporized precursor material 36 enters the isolation chamber 28.Isolation chamber 28 isolates the vaporized precursor material 36 fromthe vapor region 18. As the vaporized precursor material 36 continues totravel down the precipitation conduit 20, it eventually contacts thequench fluid stream 34 being discharged by the quench fluid port 30provided on the J-shaped outlet end 58 of quench fluid tube 54. Thequench fluid stream 34 being discharged by the fluid port 30 isconsiderably cooler than the vaporized precursor material 36. Thisresults in the rapid (i.e., substantially adiabatic) cooling of thevaporized precursor material 36. The rapid cooling results in theprecipitation of the nano-particle product 12 from the vaporizedprecursor material 36. The resulting mixture of precipitate (in the formof the nano-particle product 12) and carrier stream (e.g., air or inertor other gas atmosphere) continues to be carried down the precipitationconduit 20, whereupon it is discharged into the collection manifold 44.Thereafter, the nano-particle product 12 is ultimately captured by thefilter 40 of the product collection system 26. The remaining carrierstream passes through the pump 42 and is discharged into the surroundingatmosphere as filtered carrier stream 68.

As mentioned above, any of a wide range of liquefied gases, preferablycryogenic gases, may be used as the quench fluid to effect the rapidcooling of the vaporized precursor material 36. In the embodiment shownand described herein, liquid nitrogen is used as the quench fluid and isprovided to the inlet end 56 of quench fluid tube 54 at a pressure inthe range of about 1.3-8.3 bar (5.1-7.6 bar preferred). The accumulator62 ensures that the quench fluid (e.g., nitrogen) enters the inlet end56 as a liquid, as opposed to a liquid/gas mix or in a gaseous form.

FIG. 4 is an image of the nano-particle material 12 produced by atransmission electron microscope in a process that is commonly referredto as transmission electron microscopy (TEM). As is readily seen in FIG.4, each individual particle of the nano-particle material 12 comprises agenerally cylindrically shaped, rod-like configuration having a meanlength that is greater than its mean diameter. While the size of thenano-particle material 12 can be expressed in terms of the mean lengthor the mean diameter of the particles (e.g., as detected by transmissionelectron microscopy), it is generally more useful to express the size ofthe nano-particle material 12 in terms of surface area per unit weightdue to the correlation between size and surface area. Measurements ofparticle surface area per unit weight may be obtained by BET analysiswhich is, as mentioned above, an established analytical technique thatprovides highly accurate and definitive results. In the embodiment shownand described herein, the method and apparatus of the present inventionhas been used to produce a nano-particle material having a size in therange of about 4-44 square meters/gram (m²/g) (15-35 m²/g preferred) asmeasured in accordance with the BET analysis technique. Alternatively,other types of measuring processes may be used to determine the particlesize.

EXAMPLE 1

In this Example 1, the precursor material comprised a “technical grade”molybdic oxide (MoO₃) powder having a typical size of about 24-260microns. Such technical grade molybdic oxide powder is produced by theClimax Molybdenum Company of Fort Madison, Iowa, and is readilycommercially available therefrom. The precursor material was provided toan electrically heated sublimation furnace of the type described abovehaving a capacity to sublimate or vaporize approximately 284 kg/hr ofprecursor material. In this Example 1, the capacity of the sublimationfurnace is considerably greater than was required to produce the amountnano-particle material 12 described in this Example. This is because thesublimation furnace is used in a conventional manner to produce a highlypurified sublimed MoO₃ material in accordance with a conventionalprocess. The conventionally produced sublimed MoO₃ material comprisesparticles that are much larger than the nano-sized particles producedaccording to the present invention. Therefore, most of the sublimed orvaporized MoO₃ produced by the furnace was used in the conventionalprocess, with only a small portion being drawn-off through theprecipitation conduit to produce the nano-particle material inaccordance with the method and apparatus of the present invention.

A precipitation conduit having the configuration and dimensions of theprecipitation conduit described above was mounted within the vaporregion contained within the sublimation furnace. The precipitationconduit was connected to a collection manifold which was connected to aproduct collection apparatus. The inlet end of the quench fluid tube wasconnected to a supply of quench fluid (e.g., liquid nitrogen) inaccordance with the description provided herein. The technical gradeMoO₃ precursor material was fed into the sublimation furnace in acontinuous manner by a screw type conveyer system. Once within thefurnace, the MoO₃ precursor material was heated to a temperature ofabout 1100° C. which was sufficient to sublime the MoO₃ precursormaterial. The pump associated with the product collection apparatus wasthen turned on. As mentioned above, the pump has a capacity of about2831 liters/minute. Liquid nitrogen was utilized as the quenching fluidand was introduced into the inlet end of the quench fluid tube at apressure of about 1.3 bar. An accumulator was used to ensure that thenitrogen entered the quench fluid tube as a liquid. Once the nitrogenflow was initiated, the apparatus started to produce the nano-particlematerial, which was thereafter captured by the filter assemblyassociated with the product collection apparatus. The flow-rate of theliquid nitrogen quench fluid was such that the temperature of thecarrier stream containing the nano-particle product 12 as measured bythe thermocouple positioned within the precipitation conduit 20 wasmaintained in the range of about 37°-54° C. The apparatus was operatedin this manner for a time period of about 120 minutes, which resulted inthe production of about 2.26 kg of nano-particle material.

Another embodiment of the invention 110 is shown in FIG. 5. The secondembodiment 110 is similar to the first embodiment 10 described above,but includes additional elements, alternative configurations, andprocess steps that allow the second embodiment 110 to be usedadvantageously to produce nano-particles 112 having generally larger BETnumbers.

With reference now primarily to FIG. 5, the second embodiment 110 ofapparatus for producing nano-particles is shown and described herein asit may be used to produce nano-particles 112 of molybdenum oxide (MoO₃)from a precursor material 114. Of course, and as was the case for thefirst embodiment 10 already described, the second embodiment 110 alsomay be used to produce nano-particles of other vaporizable or sublimablematerials, as would be obvious to persons having ordinary skill in theart after having become familiar with the teachings of the presentinvention.

The apparatus 110 for producing nano-particles 112 may comprise asublimation furnace 116. In the embodiment shown and described herein,the sublimation furnace 116 may be substantially identical to thesublimation furnace 16 described above for the first embodiment and maybe define at least one vapor region 118. A precipitation conduit 120having an inlet end 122 and an outlet end 124 extends into the vaporregion 118 so that the inlet end 122 of precipitation conduit 120 isexposed to vaporized (e.g., sublimated) material 136 contained withinthe vapor region 118 of furnace 116. The outlet end 124 of precipitationconduit 120 is connected to a product collection apparatus 126 whichcollects the nano-particle product 112. In one embodiment, theprecipitation conduit 120 is also provided with a service opening 123 toallow convenient access to an interior region 129 defined by theprecipitation conduit 120. The service opening 123 may be closed by asuitable removable fitting, such as an OPW-type fitting 157.

The inlet end 122 of precipitation conduit 120 defines an isolationchamber 128 within which is provided a quench fluid port 130. The quenchfluid port 130 is fluidically connected a quench fluid supply apparatus190, which supplies a quench fluid 132 in a gas state and a quench fluidin a liquid state, as will be described in greater detail below. Afterthe quench fluid 132 in the gas and liquid states are combined, thequench fluid 132 is discharged by the quench fluid port 130 as a quenchfluid stream 134. As was already described for the first embodiment 10,the quench fluid stream 134 of the second embodiment 110 rapidly coolsthe vaporized material 136 flowing through the precipitation conduit120, resulting in the precipitation of the nano-particle material 112.The precipitated nano-particle material 112 continues to be carriedalong the precipitation conduit 120 to the product collection apparatus126.

The precipitation conduit 120 may comprise a generally elongate,pipe-like member 146 that defines the inlet end 122, the outlet end 124,and the service opening 123 of precipitation conduit 120. However,unlike the precipitation conduit 20 for the first embodiment 10, theprecipitation conduit 120 of the second embodiment 110 is not providedwith an outer pipe-like member (e.g., member 48).

The pipe-like member 146 comprising precipitation conduit 120 may havedimensions that are commensurate with the size (i.e., desired productioncapacity) of the apparatus 110 for producing nano-particles. In theembodiment shown and described herein, the pipe-like member 146 has aninside diameter of about 76.2 mm, a wall thickness of about 7.6 mm and alength of about 1524 mm. Approximately 609.6 mm of the inlet end 122 ofthe pipe-like member 146 extends into the furnace 116.

The pipe-like member 146 comprising precipitation conduit 120 may befabricated from any of a wide variety of materials (e.g.,high-temperature alloys and stainless steels) suitable for the intendedapplication. By way of example, in one preferred embodiment, thepipe-like member 146 is fabricated from high-temperature steel (e.g.,type RA300) since the inlet end 122 of pipe-like member 146 is exposedto the high temperatures in the vapor region 118 of sublimation furnace116.

The precipitation conduit 120 is provided with the quench fluid port 130suitable for discharging the quench fluid stream 134 into the pipe-likemember 146 comprising precipitation conduit 120. In the embodiment shownand described herein, the quench fluid port 130 may comprise an elongatetube-like member or quench fluid tube 154 having a branched inlet end156 and a J-shaped outlet end 158. The branched inlet end 156 isfluidically connected to the quench fluid supply apparatus 190 andreceives the quench fluid 132 in both the gas state and the liquid statein the manner that will be described in greater detail below. TheJ-shaped outlet end 158 of quench fluid tube defines the quench fluidport 130 and is positioned within the isolation chamber 128 so that thequench fluid port 130 is directed toward the downstream or outlet end124 of precipitation conduit 120. Consequently, the quench fluid stream134 discharged by the quench fluid port 130 is directed generally towardthe outlet end 124 of precipitation conduit 120.

As mentioned above, the branched inlet end 156 of quench fluid tube 154is fluidically connected to the quench fluid supply apparatus 190. Morespecifically, in the embodiment shown and described herein, a gas quenchfluid inlet portion 184 of branched inlet end 156 is fluidicallyconnected to a first supply 200 of quench fluid 132 in the gas state,whereas a liquid quench fluid inlet portion 186 of branched inlet end156 is connected to a second supply 202 of quench fluid 132 in theliquid state. In the embodiment shown and described herein, the firstsupply 200 of quench fluid 132 in the gas state and the second supply202 of quench fluid 132 in the liquid state 202 are contained with anaccumulator 162 that is fluidically connected to a supply of quenchfluid 132. Accumulator 162 functions as a separator, separating thequench fluid 132 into a gas-state portion (e.g., first supply 200) and aliquid-state portion (e.g., second supply 202). The gas-state portion(e.g., supply 200) and the liquid state portion (e.g., supply 202) areseparated in accumulator 162 by a gas/liquid interface 135. Accordingly,accumulator 162 ensures that the quench fluid 132 is delivered to thebranched inlet 156 of quench fluid tube 154 in both the gas state andthe liquid state. Alternatively, of course, other arrangements may beused to provide to the branched inlet end 156 of quench fluid tube 154the quench fluid 132 in both the gas and liquid states, as would beobvious to persons having ordinary skill in the art after having becomefamiliar with the teachings of the present invention.

A first valve 139 is connected between the first supply 200 of quenchfluid 132 in the gas state and the gas quench fluid inlet portion 184 ofbranched inlet 156. A second valve 137 is connected between the secondsupply 202 of quench fluid 132 in the liquid state and the liquid quenchfluid inlet portion 186 of branched inlet 156. A valve control system220 operatively connected to the first and second valves 139 and 137 maybe used to operate or control the positions of the first and secondvalves 139 and 137 in a manner to be described in greater detail below.

The apparatus 110 is also provided with a temperature sensor orthermocouple 155 provided within the interior region 129 ofprecipitation conduit 120. The temperature sensor or thermocouple 155senses the temperature of the carrier stream containing thenano-particle product 112 and produces an output signal 171 relatedthereto. In the embodiment shown and described herein, the distal end153 of the thermocouple 155 is highly responsive to temperature changesand is located at a position about 914 mm downstream of the quench fluidport 130. Therefore, the temperature sensed by the thermocouple 155corresponds to the temperature of the carrier stream containing thenano-particle product 112 at about that location.

The temperature sensor or thermocouple 155 is operatively connected tothe valve control system 220 so that the valve control system 220receives the output signal 171 from the temperature sensor 155. Thevalve control system 220 utilizes the output signal 171 from temperaturesensor 155 to operate the valve 137 in order to control the temperaturein the precipitation conduit 120, or, more precisely, the temperature ofthe carrier stream containing the nano-particle product 112 that flowsover the distal end 153 of temperature sensor 155. In the embodiment 110shown and described herein, a desired range temperature range for thecarrier stream and suspended nano-particle material 112 is in the rangeof about 32.3°-54.4° C. (48° C. preferred).

The apparatus 110 is also provided with a pressure sensor 159 that isoperatively associated with the branched inlet end 156 of the quenchfluid tube 154. The pressure sensor 159 senses the pressure of thequench fluid 132 contained in the branched inlet end 156 of the quenchfluid tube 154 and produces an output signal 173 related thereto. Thepressure sensor 159 is operatively connected to the valve control system220 so that the valve control system 220 receives the output signal 173from the pressure sensor 159. The valve control system 220 utilizes theoutput signal 173 from pressure sensor 159 to operate the first valve139 in order to control the pressure of the quench fluid 132 containedin the branched inlet end 156 of quench fluid tube 154. In theembodiment shown and described herein, a desired pressure range for thequench fluid 132 contained in the branched inlet end 156 of quench fluidtube 154 is in the range of about of 2-5 bar.

The location of the quench fluid port 130 within the precipitationconduit 120 has some influence on the sizes of the nano-particles 112produced by the apparatus 110 according to the present invention. Forexample, moving the location of the fluid port 130 closer to the inletend 122 of precipitation conduit 120 generally results in largernano-particles 112 being produced. Conversely, moving the location ofthe fluid port 130 away from the inlet end 122 generally results insmaller nano-particles 112. However, other factors can also affect theparticle size. For example, locating the heating elements (e.g., heatingelements 50, FIG. 1) of the furnace (e.g., 116) within close proximityto precipitation conduit 120 and thereby subjecting precipitationconduit 120 to greater radiant energy tends to result in the productionof smaller nano-particles 112 with larger BET numbers. In addition,smaller nano-particles can be produced even when the fluid port 130 ispositioned closer to the inlet end 122 of precipitation conduit 120 byincreasing the flow rate of the product collection device 126. That is,higher flow rates (e.g., liters/minute) will result in a higher velocityflow within the precipitation conduit 120. Of course, the velocitywithin the precipitation conduit 120 can also be changed by varying theinside diameter of the precipitation conduit 120.

Since the sizes of the nano-particles produced by the apparatus of thepresent invention are related to several structural and operationalparameters of the invention, as described herein, the present inventionshould not be regarded as limited to any particular parameters or rangeof parameters for any given structural or operational configuration.However, by way of example, in one preferred embodiment, the quenchfluid port 130 is positioned within the precipitation conduit 120 sothat quench fluid port 130 is located about 300 mm from the inlet end122 of precipitation conduit 120. This position of the quench fluid port130, combined with the other parameters specified herein, will result inthe formation of a nano-particle product substantially as describedherein.

As mentioned above, the apparatus 110 is also provided with a collectionmanifold 144. Collection manifold 144 serves as a convenient means fordirecting the nano-particles 112 into the product collection system 126.In the embodiment illustrated in FIG. 5, the collection manifold 144defines an interior chamber 164 having an outlet end 166 that isconnected to the production collection system 126. The collectionmanifold 144 may be fabricated from any of a wide range of materialssuitable for the intended application, as would be obvious to personshaving ordinary skill in the art after having become familiar with theteachings of the present invention. By way of example, in one preferredembodiment, the collection manifold 144 is fabricated form type SAE 316stainless steel, although other mild steel alloys, ceramics, or othersuitable materials may also be used.

The product collection system 126 may comprise a blower or pump 142 andfilter assembly 140. The blower or pump 142 draws a vaporized precursormaterial 136 through the precipitation conduit 120, the collectionmanifold 144 and filter assembly 140. More precisely, the vaporizedmaterial 136 is converted within the precipitation conduit 120 into acarrier stream having the nano-particle material 112 suspended therein.The carrier stream containing the suspended nano-particle material 112continues to be drawn through the precipitation conduit 120 under theaction of pump 142, ultimately reaching the filter assembly 140. Thefilter assembly 140 removes the nano-particle material 112 from thecarrier stream. The carrier stream is then discharged into thesurrounding atmosphere as a filtered carrier stream 168. The filterassembly 140 may be harvested from time to time to remove the capturednano-particle material 112.

The blower or pump 142 utilized in the product collection system 126 maycomprise any of a wide range of air pump devices that are well-known inthe art and readily commercially available. By way of example, in onepreferred embodiment, the pump 142 comprises a centrifugal blower havinga capacity of about 8400 (e.g., 8495) liters per minute. Alternatively,the pump 142 may have either a larger or smaller capacity depending onthe intended production capacity of the nano-particle productionapparatus 110. In another embodiment, the pump 142 may be provided witha variable capacity to allow the user to vary the flow rate of the pump142 to more easily effect certain changes in the sizes of thenano-particle material 112.

The filter assembly 140 may comprise any of a wide range devicessuitable for removing small particles from an air stream. By way ofexample, in the embodiment shown and described herein, the filterassembly 140 comprises a particulate filter medium fabricated fromGore-Tex®. The filter material should be sufficiently fine so that itwill capture substantially all of the nano-particle material 112 exitingthe collection manifold 144. However, since filters for capturing suchnano-sized particles are well-known in the art and could be easilyprovided by persons having ordinary skill in the art after having becomefamiliar with the teachings of the present invention, the filterutilized in one preferred embodiment of the present invention will notbe described in further detail herein.

In an alternative arrangement, the filter assembly 140 may comprise aliquid scrubber-type filter wherein the nano-particle material 112 iscollected by bubbling the carrier stream and nano-particle material 112through a liquid (e.g., alcohol), although other liquids may be used.The liquid captures the nano-particle material which may thereafter beremoved from the liquid by conventional techniques. Still otherfiltering devices and processes are possible and could be used tocapture and remove the nano-particle product 112 from the carrierstream, as would be obvious to persons having ordinary skill in the artafter having become familiar with the teachings of the presentinvention. Consequently, the present invention should not be regarded aslimited to the particular product collection apparatus shown anddescribed herein.

The apparatus 110 may be operated in accordance with the followingmethod in order to produce nano-particles 112 of MoO₃. The precursormaterial 114 may be fed into the sublimation furnace 116 in either acontinuous manner or in batches. In the embodiment shown and describedherein, the precursor material 114 is fed into the furnace 116 in acontinuous manner by a screw-type conveyer system (e.g., conveyer system60, FIG. 1). Once the precursor material 114 is delivered to thesublimation furnace 116, the sublimation furnace 116 heats the precursormaterial 114 to a temperature of at least about 800° C. (with optimumresults being obtained within a temperature range of about 1093°-1260°C.), which is sufficient to sublime the MoO₃ precursor material 114,resulting in the product of a vaporized or sublimed precursor material136. Sublimation of the precursor material 114 allows the production ofa highly purified nano-particle product 112.

The sublimed or vaporized precursor material 136 may be combined with acarrier gas 138, such as air or any other desired atmosphere, to assistin the flow of the vaporized or sublimed precursor material 136 into theinlet end 122 of the precipitation conduit 120. Upon being drawn intothe inlet end 122 of precipitation conduit 120, the vaporized precursormaterial 136 enters isolation chamber 128. Isolation chamber 128isolates the vaporized precursor material 136 from region 118. As thevaporized precursor material 136 continues to travel down theprecipitation conduit 120, it eventually contacts the quench fluidstream 134 being discharged by the quench fluid port 130 provided on theJ-shaped outlet end 158 of quench fluid tube 154. The quench fluidstream 134 being discharged by the fluid port 130 is considerably coolerthan the vaporized precursor material 136. This results in the rapid(i.e., substantially adiabatic) cooling of the vaporized precursormaterial 136. The rapid cooling results in the precipitation of thenano-particle product 112 form the vaporized precursor material 136. Theresulting mixture of precipitate (in the form of the nano-particleproduct 112) and carrier stream (e.g., air or inert or other gasatmosphere) continues to be carried down the precipitation conduit 120,whereupon it is discharged into the collection manifold 144. Thereafter,the nano-particle product 112 is ultimately captured by the filter 140of the production collection system 126. The remaining carrier streampasses through the pump 142 and is discharged into the surroundingatmosphere as filtered carrier stream 168.

As mentioned above, the quench fluid stream 134 discharged by the quenchfluid port 130 is formed by mixing quench fluid 132 in a gas state(e.g., from the first supply 200) and quench fluid 132 in a liquid state(e.g., from the second supply 202) at the branched inlet end 156 ofquench fluid tube 154. In addition, the valve control system 220operates the valves 139 and 137 in order to control the temperature ofthe carrier stream containing the nano-particle product 112 and thepressure of the quench fluid 132 entering the branched inlet end 156 ofquench fluid tube 154. More specifically, the amount of quench fluid 132in the liquid state (e.g., from second supply 202) that is allowed toenter the branched inlet end 156 of quench fluid tube 154 affects thetemperature of the carrier stream containing the nano-particle product112 flowing in the precipitation conduit 120. Accordingly, the valvecontrol system 220 utilizes the output signal 171 from the temperaturesensor 155 to control the position of valve 137, thereby varying theamount of quench fluid 132 in the liquid state entering branched inletend 156 of quench fluid tube 154. Generally speaking, larger amounts ofquench fluid 132 in the liquid state will result in lower temperaturesof the carrier stream containing the nano-particle material 112, whereassmaller amounts of quench fluid 132 in the liquid state will result inhigher temperatures of the carrier stream containing the nano-particlematerial 112. The control system 220 operates the valve 137 as necessaryto maintain the temperature of the carrier stream containing thenano-particle material 112 within the range specified herein.

The pressure of the quench fluid 132 in the branched inlet end 156 ofquench fluid tube 154 is controlled by varying the amount of quenchfluid 132 in the gas state (e.g., from supply 200) that is allowed toenter the branched inlet end 156. The valve control system 220 utilizesthe output signal 173 from the pressure sensor 159 to control theposition of valve 139, thereby varying the amount of quench fluid 132 inthe gas state entering the branched inlet end 156 of quench fluid tube154. Generally speaking, larger amounts of quench fluid 132 in the gasstate will result in higher pressures, whereas smaller amounts of quenchfluid 132 in the gas state will result in lower pressures. The controlsystem 220 operates the valve 139 as necessary to maintain the pressureof the quench fluid 132 in the branched inlet end 156 of quench fluidtube 154 within the range specified herein. In this regard, it should benoted that the pressure of the quench fluid 132 in the branched inletend 156 is also affected to some degree by the amount of quench fluid132 in the liquid state that is allowed to enter the branched inlet end156. That is, the operation of valve 137 will also affect the pressureof the quench fluid 132 in the branched inlet end 156. However, primarycontrol of the pressure of the quench fluid 132 in the branched inletend 156 is accomplished by controlling valve 139.

FIG. 6 is an image produced by a transmission electron microscope of thenano-particle material 112 produced by apparatus 110 shown and describedherein. The method and apparatus of the present invention has been usedto produce a nano-particle material having a size in the range of about15-68 square meters/gram (m²/g) (55 m²/g preferred) as measured inaccordance with the BET analysis technique. Alternatively, other typesof measuring processes may be used to determine the particle size.

EXAMPLE 2

In this Example 2, the precursor material 114 comprised a “technicalgrade” molybdic oxide (MoO₃) powder having a typical size of about24-260 microns. Such technical grade molybdic oxide powder is producedby the Climax Molybdenum Company of Fort Madison, Iowa, and is readilycommercially available therefrom. The precursor material 114 wasprovided to an electrically heated sublimation furnace (e.g., 116) ofthe type described above having a capacity to sublimate or vaporizeapproximately 284 kg/hr of precursor material. It should be noted thatthe capacity of the sublimation furnace is considerably greater than wasrequired to produce the amount nano-particle material 112 described inthis Example 2. This is because the sublimation furnace is used in aconventional manner to produce a highly purified sublimed MoO₃ materialin accordance with a conventional process. The conventionally producedsublimed MoO₃ material comprises particles that are much larger than thenano-sized particles produced according to the present invention.Therefore, most of the sublimed or vaporized MoO₃ produced by thefurnace was used in the conventional process, with only a small portionbeing drawn-off through the precipitation conduit 120 to produce thenano-particle material in accordance with the method and apparatus ofthe present invention.

A precipitation conduit having the configuration and dimensions of theprecipitation conduit 120 shown in FIG. 5 and described herein wasmounted within the vapor region contained within the sublimationfurnace. The precipitation conduit was connected to a collectionmanifold which was connected to a product collection apparatus. Thetechnical grade MoO₃ precursor material was fed into the sublimationfurnace in a continuous manner by a screw type conveyer system. Oncewithin the furnace, the MoO₃ precursor material was heated to atemperature of about 1100° C. which was sufficient to sublime the MoO₃precursor material. The pump associated with the product collectionapparatus was then turned on. As mentioned above, the pump has acapacity of about 8495 liters/minute. The branched inlet end of thequench fluid tube was connected to a quench fluid supply apparatus 190which supplied nitrogen quench fluid 132 in a gas state and in a liquidstate in accordance with the description provided herein. The valvecontrol system 220 was used to maintain the pressure of the quench fluid132 in the branched inlet end 156 at about 4.13 bar. Once the combinedliquid and gaseous nitrogen flow was initiated, the apparatus started toproduce the nano-particle material, which was thereafter captured by thefilter assembly associated with the product collection apparatus. Thevalve control system 220 was used to maintain the temperature of thecarrier stream containing the nano-particle product 112 at about 48° C.The apparatus was operated in this manner for a time period of about 480minutes, which resulted in the production of about 29 kg ofnano-particle material.

It is readily apparent that the apparatus and process discussed hereinmay be used to produce large quantities of MoO₃ nano-particle materialwith much simpler apparatus and without being overly sensitive tocertain process control parameters. Consequently, the claimed inventionrepresents an important development in nano-particle technology ingeneral and to molybdenum nano-particle technology in particular. Havingherein set forth preferred embodiments of the present invention, it isanticipated that suitable modifications can be made thereto which willnonetheless remain within the scope of the present invention. Therefore,it is intended that the appended claims be construed to includealternative embodiments of the invention except insofar as limited bythe prior art.

1. A nano-particle of MoO₃ having a surface area in the range of 33 toabout 68 m²/g as determined by BET.
 2. The nano-particle of claim 1,wherein the nano-particle of MoO₃ further has a generally cylindricallyshaped rod-like non-hollow configuration.
 3. The nano-particle of claim2, wherein the configuration has a mean length that is greater than amean diameter.
 4. The nano-particle of claim 3, wherein thenano-particle of MoO₃ further has blunt ends.
 5. The nano-particle ofclaim 1, wherein the nano-particle of MoO₃ further has a rod-likenon-hollow configuration.
 6. A nano-particle of MoO₃ having a surfacearea in the range of 45 to about 68 m²/g as determined by BET.
 7. Thenano-particle of claim 6, wherein the nano-particle of MoO₃ further hasa generally cylindrically shaped rod-like non-hollow configuration. 8.The nano-particle of claim 7, wherein the configuration has a meanlength that is greater than a mean diameter.
 9. The nano-particle ofclaim 8, wherein the nano-particle of MoO₃ further has blunt ends. 10.The nano-particle of claim 1, wherein the nano-particle of MoO₃ furtherhas a rod-like non-hollow configuration.